Someone in another thread was asking about changing the 9150/80 from 2X the bus speed ( 2 X 40MHz = 80 MHz) to 3X and running the bus more slowly.I have an 80MHz version.
The PPC601 seems to need a clock buffer chip which can multiply the system clock signal by 3 for it. I may be wrong about the following, because it's from memory, but if you look at the lower left corner of bigD's photo above, then move one chip to the right (no, not the oscillator, the next one to the right), you'll see a set of unused pads around a smaller chip. If I'm not mistaken, that smaller chip is the clock buffer for the machine and the unused pads are where the ICS9178 would go if this were a clock tripling machine, instead of a clock doubling machine. All the speed bumped PM8100s (100, 110) had the ICS9178 as well.
Adding an ICS9178 is also how one converts the Turbo601/66 into a Turbo601/100 (well more like 90 to 96).